<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        @property --angle{
            syntax: "<angle>";
            initial-value: 0deg;
            inherits:false;
        }
        .element{
        width:400px;
        height:400px;
        background-image:conic-gradient(from var(--angle),red,blue,red );
        animation:1s spin linear infinite;
        }
        @keyframes spin {
            from{
                --angle: 0deg;
            }
            to{
                --angle: 360deg;
            }
        }
    </style>
</head>
<body>
    <div class="element"></div>
</body>
</html>